1. Field of the Invention
The present invention relates to an electric powered vehicle in which a PWM driven motor is mounted.
2. Description of Related Art
There are electric powered vehicles which travel with a drive force of a motor, and the electric powered vehicles include an electric vehicle (EV) in which an engine is not mounted, and a hybrid vehicle (HV) in which both of a motor and an engine are mounted.
In such an electric powered vehicle, normally, a battery is mounted, and electric power from the battery is converted to a desired AC current by an inverter to drive the motor. In this case, output torque of the motor should be controlled to follow requested torque of the vehicle according to an accelerator depression amount. Accordingly, in a normal case, switching of the inverter is controlled by a PWM control signal, thereby obtaining motor output torque according to requested torque of the vehicle.
Here, PWM control of the motor performs sine wave control where a drive waveform normally becomes a sine wave; however, when a motor output is great and a modulation rate is high, overmodulation control and square wave control are performed.
In the PWM control, if the overmodulation control is performed, the drive waveform does not become a sine wave, and a disturbance occurs in the drive waveform. During high-speed traveling, when torque output is low in a state where the motor rotation speed is high, a fine current pulse occurs, and a surge becomes great. In particular, when torque output is low, the amount of current is small; therefore, a motor current zero-crosses multiple times due to a disturbance in the motor current, and a surge is likely to become extremely great.
If the surge is extremely great, the withstand voltage of the motor should be made great to that extent, and the build of the motor becomes great. Accordingly, it is desirable to suppress the occurrence of a great surge.
Japanese Patent Application Publication No. 2014-082855 (JP 2014-082855 A) describes controlling a transmission gear ratio in order to prevent the occurrence of noise during overmodulation control. However, in JP 2014-082855 A, since gear shift control is performed so as to avoid the entire overmodulation control, unintended gear shift control by a user occurs frequently, and the user is likely to feel a sense of discomfort.